Ionic liquids have attracted special attention for the past several years, owing to their potential uses as electrolytes for a variety of electrochemical devices such as lithium secondary batteries, solar cells, actuators, electric double-layer capacitors and the like, reaction media, and catalysts for organic syntheses. Compared with conventional organic liquid electrolytes, the main advantages of ionic liquids as electrolytes are flame retardance, non-volatility and high thermal stability. Bistrifluoromethylsulfonylimide ([(CF3SO2)2N]−) and tetrafluoroborate (BF4−) have attracted attention as anions for most of the ionic liquids reported thus far, because of their high electrochemical stabilities and thermal stabilities (PTL 1 and PTL 2).
Moreover, anions represented by [(nCnF2+1)BF3]− (wherein n is 1, 2, 3, or 4) of ionic liquids are also known (PTL 3).
However, ionic liquids containing these anions have suffered from problems such as, in particular, low conductivities at low temperatures.